Process for the isolation of polyvinyl chloride



itreated to obtain the solid polymer. end the emulsion may be brokendown, i. e. co-

Patented May 1, 1951 PROCESS FOR THE ISOLATION OF POLYVINYL CHLORIDEPaul Halbig, Fribourg, Switzerland No Drawing. Application February 27,1948, Serial No. 11,334. In Switzerland March 9, 1 943 SeetionLPnblicLaw 690, August 8, 1946 Patent expires March 9, 1963 5 Claims.

This invention relates to improvements in a process for the separationof polyvinyl chloride from emulsions containing the same.

It is well known in the art to polymerise vinyl chloride in the presenceof water, emulsifying agents and catalysts, so as to obtain an aqueousemulsion of polyvinyl chloride. The resulting emulsion is, if not beingused as such, further To such agulated, e. g. by adding electrolytes,whereby the polymer is precipitated, and the powder obtained separatedfrom the liquid phase, washed,

and dried, or the emulsion may be dehydrated, e. g. in a spray dryer, soas to obtain a dry product in a single step. If the process is performedaccording to the method of direct dehydration or drying, the solidpolymer will contain all the foreign substances which were present inthe emulsion and more particularly the emulsifying agent and thecatalyst. If the separation is performed by coagulation, the polymerwill precipi tate in most cases in form of fine particles which may befiltered and washed out only with difficulty, and which will retainlarge amounts of water and residual electrolytes. In both cases largeamounts of water must be evaporated in order to obtain the polymers indry state.

It now has been found that the coagulated polymers may be easilyconverted into a readily filtrable, washable and water-repellent form,when the coagulated emulsion is treated with an organic liquid which isinsoluble or substantially insoluble in water. This treatment is bestperformed by intensively stirring the emulsion admixed with the organicliquid. Th organic liquid should have substantially no dissolving effecton polyvinyl chloride at the temperatures prevailing during thetreatment, and should be easily removable from the mixture. Substanceswhich are particularly adapted for such purpose are ether, chloroform,benzene and the like. A substance of special usefulness is the liquidmonomeric vinyl chloride. By choosing certain amounts of the organicliquid and by controlling the time and temperature of the treatment, thewater-repellent properties of the polymer may be enhanced to such adegree, that products are obtained which, after a simple centrifugalseparation, do not contain more than about of water.

The present invention will now be described in being limited thereto.The parts are by weight.

Example 1000 parts of a polyvinyl chloride-emulsion as prepared, e. g.according to the process of the copending Swiss Patent 239,764, andcontaining about 25% of polyvinyl chloride are coagulated by addition of10 gr. of magnesium sulfate. The fairly thick slurry is then stirredduring about 10 minutes in the presence of parts of vinyl chloride, at atemperature of about 30 C. and in a pressure vessel. The vinyl chloridethen is blown off at a temperature of about 15 C. The polymer now hasthe form of a heavy, gritty, water-repellent powder, which can easily beseparated from the liquid phase, centrifuged and washed until it is freefrom any remaining electrolyte. In this manner there will easily beobtained a product having a water content of only 20% and which afterdrying yields a pure powdery polymer. When the treatment is performed atsomewhat higher temperatures, e. g. at about 50 C., the polymer formsbead-like aggregations which, after centrifugation, contain only about5% of water. After drying, these aggregations may easily be crushed to afine powder, e. g. by finger.

Generally, the organic liquids, which are insoluble orsubstantiallyinsoluble in water, are added to the emulsion, as describedabove, after the latter has undergone coagulation, i. e. immediatelybefore the treatment. It may also be advisable, however, especially whenthe substances are to remain in the polymer, to add these substancesbefore the emulsion is coagulated, in which case the actualtreatment, 1. e. the intensive agitation or stirring of the liquidmixture, also is performed after the coagulation of the emulsion. Whenthe treating liquid is for instance monomeric vinyl chloride, it may bederived from the polymerisation process itself by interrupting thereaction as long as there is a suificient amount of monomeric vinylchloride present in the mixture. Such interruption may be effected bycooling the mixture. The emulsion containing monomeric vinyl chloride,is then coagulated by adding suitable substances or by other means, e.g. by cooling or treatment with supersonic vibrations, and then stirredfor some time, whereupon the monomeric vinyl chloride is blown off, andthe polymer further treated as described above. It may be advisable tofilter the polymer under pressure of vinyl chloride.

It is essential that the coagulated polymer is subjected to a thoroughtreatment with the organic liquid, so that the particles of the polymerattain the desired water-repellent character.

What I claim is:

1. A process for the isolation of polyvinyl chloride from a coagulatedaqueous emulsion thereof, comprising the steps of intensively stirringthe coagulated aqueous emulsion with a liquid essentiallywater-insoluble organic compound which has substantially no dissolvingeffect.

on polyvinyl chloride at the temperatures prevailing during thestirring, continuing, the said stirring until the polymer has acquireda. degree of water-repellency such that, after simple centrifuging, itsWater content does not exceed more than about 20%, then removing theorganic liquid from the stirred coagulated emulsion, and finallyisolating the polymer from the remaining aqueous mixture.

2. A process according to claim 1, wherein the organic compound ismonomeric liquid vinyl chloride.

3. A process according to claim 2, wherein the coagulated aqueousemulsion contains about 25% of polyvinyl chloride and the monomericliquid emulsion by interrupting the polymerization prior to completionthereof.

PAUL HALBIG.

REFERENCES CITED The following references are of record in the file of.this patent:

UNITED STATES PATENTS Number Name Date 2,068,424 Mark Jan. 19, 19372,458,636 Plambeck Jan; 11, 1949

1. A PROCESS FOR THE ISOLATION OF POLYVINYL CHLORIDE FROM A COAGULATEDAQUEOUS EMULSION THEREOF, COMPRISING THE STEPS OF INTENSIVELY STIRRINGTHE COAGULATED AQUEOUS EMULSION WITH A LIQUID ESSENTIALLYWATER-INSOLUBLE ORGANIC COMPOUND WHICH HAS SUBSTANTIALLY NO DISSOLVINGEFFECT ON POLYVINYL CHLORIDE AT THE TEMPERATURE PRREVAILING DURING THESTIRRING, CONTINUING THE SAID STIRRING UNTIL THE POLYMER HAS ACQUIRED ADEGREE OF WATER-REPELLENCY SUCH THAT, AFTER SIMPLE CENTRIFUGING, ITSWATER CONTENT DOES NOT EXCEED MORE THAN ABOUT 20%, THEN REMOVING THEORGANIC LIQUID FROM THE STIRRED COAGULATED EMULSION, AND FINALLYISOLATING THE POLYMER FROM THE REMAINING AQUEOUS MIXTURE.